1. Field of the Invention
The present invention relates to a moving mechanism for moving a plurality of inner and outer cylinders provided in a multiple manner in the axial direction relative to each other and, more particularly, to a moving mechanism used in, e.g., a lens barrel for a camera.
2. Related Background Art
Conventionally, as a mechanism for moving a plurality of cylinders in the axial direction relative to each other, a helicoid mechanism is known as described in Japanese Patent Laid-Open No. 10-31150, in which either one of a root and crest is helically formed on the inner surface of an outer cylinder, and the other one is formed on the outer surface of an inner cylinder. One of the outer and inner cylinders is rotated with respect to the other, thereby transforming a rotary motion into a rectilinear motion.
According to the helicoid mechanism described in this reference, a large-width portion is formed in part of the root by widening the width of the root. The amount of movement of the outer and inner cylinders relative to each other is increased by using the large-width portion.
In the above helicoid mechanism, the degree of freedom of the movement of the outer and inner cylinders relative to each other is small. More specifically, in the above helicoid mechanism, it is certain that the amount of movement of the outer and inner cylinders relative to each other can be increased with respect to rotation of the outer or inner cylinder by utilizing the large-width portion formed in part of the root. As shown in FIG. 6 of this reference, since the crest (34b) is formed adjacent to the root, the amount of increase in the relative movement is limited to a certain level due to the position of the crest and the like, and becomes small. Also, it is difficult to conversely decrease the amount of movement of the outer and inner cylinders relative to each other with respect to movement obtained by helicoid.
The present invention has been made in order to solve the above drawbacks, and has an object to provide a moving mechanism for a cylinder in which the movement of inner and outer cylinders relative to each other can be freely set.
According to an aspect of the present invention, there is provided a moving mechanism in which a first helicoid thread is helically formed on an inner surface of a first cylinder, a second helicoid thread that threadably engages with the first helicoid thread of the first cylinder is helically formed on an outer surface of a second cylinder, and either one of the first and second cylinders is rotated with respect to the other cylinder, so the other cylinder is moved relative to one cylinder, wherein the moving mechanism includes a projection formed on the outer surface of the second cylinder, and a groove formed in the inner surface of the first cylinder and adapted to engage with the projection, the groove is formed parallel to the first helicoid thread in a range where the first and second helicoid threads threadably engage with each other upon movement of the first and second cylinders relative to each other, and has a nonparallel region not parallel to at least the first helicoid thread within a range where the first and second helicoid threads do not threadably engage with each other.
According to another aspect of the present invention, there is provided a moving mechanism in which a first helicoid thread is helically formed on an inner surface of a first cylinder, a second helicoid thread that threadably engages with the first helicoid thread of the first cylinder is helically formed on an outer surface of a second cylinder, and either one of the first and second cylinders is rotated with respect to the other cylinder, so the other cylinder is moved relative to one cylinder, wherein the moving mechanism includes a projection formed on the inner surface of the first cylinder, and a groove formed in the outer surface of the second cylinder and adapted to engage with the projection, the groove is formed parallel to the second helicoid thread in a range where the first and second helicoid threads threadably engage with each other upon movement of the first and second cylinders relative to each other, and has a nonparallel region not parallel to at least the second helicoid thread within a range where the first and second helicoid threads do not threadably engage with each other.
According to the present invention, a photographic lens is preferably accommodated in the first and second cylinders, and the moving mechanism is preferably used for a lens barrel for the photographic lens.
According to the present invention, the first and second cylinders engage with each other not only through the first and second helicoid threads but also through the projection and groove. Therefore, within the range where the first and second helicoid threads threadably engage with each other upon movement of the first and second cylinders relative to each other, the first and second cylinders can be precisely moved relative to each other through a helicoid mechanism comprised of the first and second helicoid threads. In the range where the first and second helicoid threads do not threadably engage with each other, the first and second cylinders can be moved relative to each other through the projection and groove by relative movement different from that by the helicoid mechanism. When a nonparallel region is formed in the groove, movement of the first and second cylinders relative to each other can be freely set.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.